1. Field of the Invention
The present invention relates to a telescope system that corrects deformation of a pedestal unit and a main reflector unit due to the wind force to improve pointing accuracy of the pedestal unit and the main reflector unit.
2. Description of the Related Art
In the field of the radio astronomy, in recent years, there has been an increasing demand for observation of submillimeter waves that are radio waves higher in frequency than millimeter waves. In performing radio astronomical observation at high frequencies, higher accuracy is required for a main reflector (a reflecting mirror) surface of an antenna and pointing and tracking of beams. On the other hand, to improve observation efficiency, an aperture of the antenna is increased and it is desired that observation can be carried out in all kinds of weather night and day.
When the aperture of the antenna is increased, deadweight deformation of the antenna increases and thermal deformation due to the solar radiation and deformation due to the wind pressure increase. Thus, it is difficult to obtain high pointing and tracking accuracy. In order to satisfy the requirement for such high pointing and tracking accuracy, it is necessary to measure in real time a pointing error of a main reflector of a telescope system and correct the pointing error. As factors affecting the pointing error of the telescope system, there are deformation of a structural portion (a pedestal unit) that supports the main reflector and elastic deformation of the main reflector itself. The deformation due to the wind pressure is the main cause of such kinds of deformation.
Conventionally, angle information of both axes of an azimuth (AZ) and an elevation (EL) of such a large telescope system is detected by an encoder and subjected to feedback control. Thus, even if the telescope system is affected by a force of the wind, it looks as if the AZ and the EL of the telescope system can be controlled according to a command value. However, actually, the pedestal affected by the wind force is deformed. Thus, the elevation axis is tilted from a reference axis or displaced to a torsion position. In the conventional large telescope system, the deformation of the pedestals and the like is not taken into account and adversely affects the pointing accuracy. Thus, the deformation is one of causes that make it impossible to attain fixed or higher pointing accuracy.
Conventionally, as a mechanism that copes with this problem, an antenna angle detector that can detect an antenna pointing error due to elastic deformation of a pedestal is proposed (see JP-A-03-3402).
FIG. 9 is a diagram of a mechanism of a conventional telescope system that can detect an antenna pointing error described in JP-A-03-3402. In FIG. 9, reference numeral 1 denotes a main reflecting mirror; 2, a pedestal unit; 29, an AZ angle detector for an antenna; 30, an EL angle detector for the antenna; 31, an EL angle detector same as the EL angle detector 30 or a mount that has a case same as that for the EL angle detector 30.
Reference numeral 32 denotes two beam generators mounted on the AZ angle detector 29 fixed to the pedestal unit 2. Reference numeral 33 denotes light position detectors for an AZ axis provided on the EL angle detector or the mount 31. Beams are irradiated on the light position detectors for an AZ axis 31 from the beam generators 32. Reference numeral 34 denotes beam generators that are provided on the EL angle detector 30 or the mount 31. Reference numeral 35 denotes light position detectors for an EL axis provided on the AZ angle detector 29. Beams from the beam generators 34 are irradiated on the light position detectors 35. The light position detectors 33 and 35 are photodiodes divided into two and are set to be sensitive only to a deviation of beams in a Y axis direction.
Operations of this system will be explained. When the pedestal unit 2 is deformed, torsion around the axes and parallel displacement occur. In the system shown in FIG. 9, the two sets of the light position detectors 33 and 35 and the beam generators 32 and 34 are provided for the AZ axis and the EL axis, respectively. Amounts of torsion around the AZ axis and the EL axis affecting a pointing error are detected by subjecting outputs of the light position detectors 33 and 35 and the beam generators 32 and 34 to arithmetic processing. The amounts of torsion of the respective axes detected in this way are added to or subtracted from angle signals detected by the EL angle detectors 30 and 31 and the AZ angle detector 29 to correct the amounts of torsion.
In the conventional antenna angle detector described above, it is logically possible to measure a pointing error of main reflecting mirror beams when torsion of the AZ axis and the EL axis due to the deformation of the pedestal unit 2 occurs. However, actually, a yoke unit, an AZ bearing, and other structure, which are not shown in the figure, are present between the beam generators 32 and 34 and the light position detectors 33 and 35. Thus, it is extremely difficult to set the light position detectors 33 and 35 not to block the beams. The beams tend to be affected by heat generation of the beam generators themselves and heat around the beam generators to cause temperature drift. This makes it difficult to determine whether an amount of thermal deformation of the pedestal unit 2 is measured or heat drift of the beams is measured.